Protesters have asked the foreign secretary for fresh action to help a Londoner facing her second Mother's Day in an Iranian jail.
Nazanin Zaghari-Ratcliffe is in prison in Tehran on spying charges she denies.
Campaigners laid 707 pebbles outside the Foreign and Commonwealth Office in Westminster to represent each day the mother-of-one has been detained.
Boris Johnson has previously said he would leave "no stone unturned" to help free Mrs Zaghari-Ratcliffe.
Campaigners said the display was to "gently remind" Boris Johnson of his "promise" to help.
Mrs Zaghari-Ratcliffe, who is British-Iranian, was arrested at Tehran Airport in 2016.
She and her husband, Richard Ratcliffe, have always said the visit was so their daughter Gabriella could meet her grandparents.
Mr Ratcliffe, from Hampstead, north London, said: "I don't think we'd ever thought it would last this long.
"Each landmark that comes is just a reminder that she's still away.
"You strip it all back, the thing she's most upset about is that she's been away from Gabriella and [has] not watched her grow up."
The foreign secretary went to Iran in December to call for Mrs Zaghari-Ratcliffe's release.
An FCO spokeswoman said: "We will not be providing a running commentary on every twist and turn."